Automatic barrier operators such as a garage door opener or gate opener are used in many homes. These operators typically require the activation of a wireless transmitter in order to open or close the barrier. However, there are times that users may forget to activate the operator to close the barrier. Alternatively, it may not be convenient or safe for the driver to remove his/her hands from the steering wheel to activate the wireless transmitter.
Conventional barrier operators include, for example, U.S. Pat. No. 6,476,732 which describes how an approaching vehicle can activate a garage door using a Global Positioning System (GPS). A similar system incorporating GPS technology is also described in U.S. Pat. No. 6,615,132. GPS may be used to locate an object on earth through communication with satellites. There are however, several disadvantages in using such technology. Although GPS systems are widely available, it is rather expensive to employ this technology for barrier control operation. Another disadvantage in implementing GPS technology for such use is accuracy. Most consumer-grade GPS receivers are accurate to only within 50 feet, which means that an error of up to 50 feet may be expected. For applications such as garage door control, such a range of error may be unacceptable. For example, if an authorized vehicle is approaching a driveway that is 40 feet long, the door may not open even if the vehicle is on the driveway, since the range of error is 50 feet. Moreover, most driveways are less than 50 feet long. There are other sources of errors such as signal multi-path, orbital errors, Ionosphere and troposphere delays, receiver clock errors etc. Therefore, there is a need for a system and method that overcomes these disadvantages.